The invention relates to battery powered electrical equipment, and in particular the invention is concerned with a battery compartment for a battery powered electrical device that accommodates different types of battery cells, which may be standard dry cells on the one hand, and rechargeable cells on the other hand.
Portable electrical or electronic devices such as camera flashes, tape recorders, games and computers usually can be powered with standard dry cell batteries, such as alkaline type battery cells of standard dimensions. It is often desired to use rechargeable battery cells with these portable devices, and these have been available in several forms.
One type of rechargeable battery cell follows the same dimensions as the alkaline battery cells, so that these cells can be used interchangeably with the throw-away dry cells. Some of these are NiCad rechargeable cells.
However, another and in some ways superior rechargeable battery in wide use comprises NiCad rechargeable cells in different dimensions, shorter in length and larger in diameter than the standard alkaline dry cells. The larger-diameter NiCad cells have greater capacity and generally are bound together and electrically connected into a unitary battery. The battery of NiCad cells is placed as a unit into a battery pack designed for this type of cells, with two output terminals of the battery engaged with appropriately placed conductors in the battery pack. When low, the NiCad battery is charged as a unit.
It has been a limitation of many conventional battery compartments and battery packs and of portable electrical devices in general, that a particular battery compartment could be served only with battery cells of one configuration,--for example either the large-diameter NiCad cells or cells having the conventional dry cell dimensions.
Some portable devices such as video cassette recorder cameras have had provision for the use of either rechargeable or non-rechargeable battery cells. This has been accomplished in some cases by the use of two different battery packs for the VCR camera--one removable pack which may be sealed and which includes a rechargeable battery such as NiCad cells; and another removable pack which can be opened to insert alkaline type dry cells. In theory this can allow the user to purchase alkaline cells on an emergency basis, if the rechargeable battery pack goes too low in charge when the camera is being used. However, in practice it requires the user to anticipate this problem and thus to have the alternate battery pack casing on hand. The user often does not anticipate this situation. The user ordinarily plans on using only the rechargeable pack, does not bring the alkaline cell case, and thus is unable to use alkaline cells when the rechargeable battery pack has lost its charge.
It would therefore be desirable in a great number of portable devices for a battery pack to be capable of receiving either a rechargeable battery or standard dry cells such as alkaline batteries. There have been, however, two problems with this approach. The alkaline dry cells are of different dimensions from those of the optimum NiCad battery pack cells; and a charging current must be prevented from being applied to the dry cells. Such a charging current is normally applied to the rechargeable battery when it is in the portable device and external power (an AC/DC converter) is being applied to the device.